Organic El device

ABSTRACT

An organic EL device having, as a cathode, a vapor deposited film containing at least one metal A selected from Pb, Sn and Bi and a metal B having a work function of 4.2 eV or less, provided by the present invention, has high chemical stability of the cathode with time and high power conversion efficiency, and is useful as a display device and a light-emitting device.

TECHNICAL FIELD

The present invention relates to an organic EL device(electroluminescence device) used as a display device or alight-emitting device.

TECHNICAL BACKGROUND

An organic EL device is constituted by placing at least a thin layer ofan organic light-emitting material (light-emitting layer) between a pairof electrodes facing to each other. In this organic EL device, electronsinjected into a light-emitting layer from a cathode directly or throughan electron-injecting layer and holes injected into the light-emittinglayer from an anode directly or through a hole-injecting layer recombinein the light-emitting layer, whereby light is emitted.

As means for improving the light emission properties of the organic ELdevice based on the above light-emitting mechanism, it is known toselect or improve the organic light-emitting material, to improve thefilm quality of the light-emitting layer or to select or improve acathode material. Of these, the means of selecting or improving thecathode material is generally aimed at the improvement of the efficiencyof injection of electrons into the light-emitting layer for improvingthe light emission properties. It is therefore being attempted to use avariety of electrically conductive metals, alloys or intermetalliccompounds having small work functions as a material for the cathode.

For example, U.S. Pat. No. 3,173,050 and U.S. Pat. No. 3,382,394disclose organic EL devices whose cathode is formed of alkali metal suchas Na-K alloy. The organic EL devices disclosed in these U.S. Patentsare desirable in that the quantum efficiency is high (see RCA ReviewVol. 30, page 322), while they are not practical since alkali metals andalloy formed of alkali metals alone are highly active and chemicallyunstable.

It is therefore variously proposed to form cathodes from metals otherthan alkali metals. For example, U.S. Pat. No. 4,539,507 discloses anorganic EL device whose cathode is formed of In. JP-A-3-231970 disclosesan organic EL device whose cathode is formed of Mg-In alloy. Further,European Patent 0278757 discloses an organic EL device provided with acathode formed of a layer containing a plurality of metals other thanalkali metals, at least one of which metals other than alkali metals hasa work function of 4 eV or less (Mg-based electrode formed of Mg and oneof Ag, In, Sn, Sb, Te and Mn, such as Mg-Ag electrode).

Further, various organic EL devices whose cathodes are formed ofmixtures of at least 11 at. % of metals having excellentelectron-injecting properties such as Li, Na, Ca and Sr with relativelystable metals such as Mg, Al, In and Sn are disclosed in Autumn Meetingheld in 1991 (Polymer Preprints, Japan, Vol. 40, No. 10, page 3,582).However, the organic EL devices disclosed in the Meeting are inferior toan organic EL device having an Mg-Ag electrode as a cathode inefficiency (power conversion efficiency).

As described above, there have been various proposals for formingcathodes from metals having electroninjecting properties, while thesecathodes are poor in chemical stability with time, and organic ELdevices having these cathodes have been unsatisfactory in powerconversion efficiency.

It is an object of the present invention to provide a novel organic ELdevice having a cathode having high stability with time and improvedpower conversion efficiency.

DISCLOSURE OF THE INVENTION

The organic EL device of the present invention which achieves the aboveobjects has a feature in that it has, as a cathode, a vapor depositedfilm containing at least one metal A selected from Pb, Sn and Bi and ametal B having a work function of 4.2 eV or less.

PREFERRED EMBODIMENTS FOR WORKING THE INVENTION

The present invention will be detailed hereinafter.

As described above, the cathode of the organic EL device of the presentinvention is formed of a vapor deposited film containing at least onemetal A selected from Pb, Sn and Bi and a metal B having a work functionof 4.2 eV or less. Specific examples of the metal B having a workfunction of 4.2 eV or less include In, Cd, Mn, Ti, Ta, Zr, La, Ca, Li,Ba, Na, Mg, Gd, K, Y and Yb. In view of the improvement inelectron-injecting properties, metals having a work function of 4.0 eVor less are preferred. Specific examples of such metals include La, Ca,Li, Ba, Na, Mg, Gd, K, Y and Yb which are all described above. As themetal B, one metal may be used or a plurality of metals may be used.

The method for forming the vapor deposited film containing the metal Aand the metal B is not specially limited. Specific examples of the abovemethod include direct alloy vapor deposition methods and multi-sourcesimultaneous vapor deposition methods, which employ any one of aresistance heating vapor deposition method, an electron beam heatingvapor deposition method, a high-frequency induction heating method, amolecular beam epitaxy method, a hot wall vapor deposition method, anion plating method, an ionized cluster beam method, a diode sputteringmethod, a diode magnetron sputtering method, a triode and tetraodeplasma sputtering methods, an ionized beam sputtering method. Foreffectively producing a cathode having a desired composition, it isparticularly preferred to employ a multi-source simultaneous vapordeposition method.

The cathode produced by forming a film as above is satisfactory so longas it contains the metal A and the metal B. The content of the metal Ain the cathode is preferably 90 to 99.999 at. %. The reason therefor isthat when the content of the metal A is 90 to 90.999 at. %, the metal Aconstitutes the matrix of the cathode and improves the chemicalstability of the cathode with time. The content of the metal A isparticularly preferably 95 to 99.99 at. %.

When a vapor deposited film of the cathode is formed by the multi-sourcesimultaneous vapor deposition method for example, the composition of thecathode can be controlled by properly setting the deposition rates ofthe metal A and the metal B. The deposition rate of the metal A is atleast 2 nm/sec., particularly at least 4 nm/sec., and the vapordeposition for the metal B is 0.5 nm/sec. or less, particularly 0. 2nm/sec or less. When two metals (e.g., Pb and Sn) or more are used asthe metal A, the total of the deposition rates of these metals forforming the metal A is preferably at least 2 nm/sec., more preferably atleast 4 nm/sec. When two metals (e.g., Mg and Ca) or more are used asthe metal B, the total of the deposition rates of these metals forforming the metal B is preferably 0.5 nm/sec. or less, particularlypreferably 0.2 nm/sec. or less. The deposition rate of the metal A isgreater than the deposition rate of the metal B as described above,whereby there can be obtained a vapor deposited film having a greatercontent of the metal A and a smaller content of the metal B. Further, bycombining the metal A and the metal B in this manner, there can beobtained a cathode having excellent electron-injecting properties. Thethickness of the so-obtained cathode is not specially limited so long asit has conductivity within the film, while the thickness is preferably10 to 400 run, particularly preferably 30 to 200 nm.

The constitution of the organic EL device of the present invention isnot specially limited so long as it has the above-described cathode. Forexample, the constitution of the organic EL device includes (1)anode/light-emitting layer/cathode, (2) anode/hole-injectinglayer/light-emitting layer/cathode, (3) anode/light-emittinglayer/electron-injecting layer/cathode, (4) anode/hole-injectinglayer/light-emitting layer/electron-injecting layer/cathode, and thelike. The organic EL device of the present invention may have any one ofthe above constitutions. Further, when the organic EL device of thepresent invention is produced, the materials for, and the method forforming, the members other than the cathode are not specially limited,and these other members may be formed from various materials by avariety of methods, as will be described later.

The organic EL device having the so-obtained vapor deposited filmcontaining the metal A and the metal B, provided by the presentinvention, not only has high chemical stability of the cathode withtime, but also has power conversion efficiency equivalent to or higherthan that of an organic EL device having an Mg-based cathode which isconsidered to have high power conversion efficiency among conventionalorganic EL devices.

The materials for, and the method for forming, the members other thanthe cathode in the organic EL device of the present invention will bedescribed below.

For example, the organic compound that can be used as a material for thelight-emitting layer is not specially limited, while there can be usedbenzothiazole, benzoimidazole and benzooxazole fluorescent brighteners,metal chelated oxinoid compounds and styrylbenzene compounds.

Specifically, the above fluorescent brighteners are disclosed, forexample, in JP-A-59-194393. Typical examples thereof includebenzooxazole fluorescent brighteners such as2,5-bis(5,7-di-tert-pentyl-2-benzooxazolyl)-1,3,4-thiadiazole,4,4-bis(5,7-tert-pentyl-2-benzooxazolyl)stilbene,4,4'-bis[5,7-di-(2-methyl-2-butyl)-2-benzooxazolyl]stilbene,2,5-bis(5,7-di-tert-pentyl-2-benzooxazolyl)thiphene,2,5-bis[5-α,α-dimethylbenzyl-2-benzooxazolyl]thiophene,2,5-bis[5,7-di-(2-methyl-2-butyl)-2-benzooxazolyl]-3,4-diphenylthiophene,2,5-bis(5-methyl-2-benzooxazolyl)thiophene,4,4'-bis(2-benzooxazolyl)biphenyl,5-methyl-2-[2-[4-(5-methyl-2-benzooxazolyl)phenyl]vinyl]benzooxazole,2-[2-(4-chlorophenyl)vinyl]naphtho[1,2-d]oxazole; benzothiazolefluorescent brighteners such as2,2'-(p-phenylenedivinylene)-bisbenzothiazole; and benzoimidazolefluorescent brighteners such as2-[2-[4-(2-benzoimidazole)phenyl]vinyl]benzoimidazole and2-[2-(4-carboxyphenyl)vinyl]benzoimidazole. Further, other usefulcompounds are listed in Chemistry of Synthetic Dyes, 1971, pages 628-637and 640.

The above chelated oxinoid compounds are disclosed, for example, inJP-A-63-295695. Typical examples thereof include 8-hydroxyquinolinemetal complexes such as tris(8-quinolinol)aluminum,bis(8-quinolinol)magnesium, bis(benzo[f]-8-quinolinol)zinc,bis(2-methyl-8-quinolinolate)aluminum oxide, tris(8-quinolinol)indium,tris(5-methyl-8-quinolinol)aluminum, 8-quinolinollithium,tris(5-chloro-8-quinolinol)gallium, bis(5-chloro-8-quinolinol)potassiumand poly[zinc(II)-bis(8-hydroxy-5-quinolinonyl)methane, anddilithiumepindolidione.

The above styrylbenzene compounds are disclosed, for example, inEuropean Patent 0319881 and European Patent 0373582. Typical examplesthereof include 1,4-bis(2-methylstyryl)benzene,1,4-bis(3-methylstyryl)benzene, 1,4-bis(4-methylstyryl)benzene,distyrylbenzene, 1,4-bis(2-ethylstyryl)benzene,1,4-bis(3-ethylstyryl)benzene, 1,4-bis(2-methylstyryl)-2-methylbenzeneand 1,4-bis(2-methylstyryl)-2-ethylbenzene.

Further, distyrylpyrazine derivatives disclosed in JP-A-2-252793 can bealso used as a material for the light-emitting layer. Typical examplesof distyrylpyrizine derivatives include 2,5-bis(4-methylstyryl)pyrazine,2,5-bis(4-ethylstyryl)pyrazine, 2,5-bis[2-(1-naphthyl)vinyl]pyrazine,2,5-bis(4-methoxystyryl)pyrazine, 2,5-bis[2-(4-biphenyl)vinyl]pyrazineand 2,5-bis[2-(1-pyrenyl)vinyl]pyrazine.

Further, polyphenyl compounds disclosed, for example, in European Patent0387715 can be also used as a material for the light-emitting layer.

In addition to the above fluorescent brighteners, metal chelated oxinoidcompounds and styrylbenzene compounds, the material for thelight-emitting layer can be also selected, for example, from12-phthaloperinone (J. Appl. Phys., Vol. 27, L713 (1988)),1,4-diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene (thus far,Appl. Phys. Lett. Vol. 56, 799 (1990)), naphthalimde derivatives(JP-A-2-305886), perylene derivatives (JP-A-2-189890), oxadiazolederivatives (JP-A-2-216791, including oxadiazole derivatives disclosedby Hamada et al., in Proceedings of No. 38th Spring Meeting 1993 TheJapan Society of Applied Physics and Related Societies), aldazinederivatives (JP-A-2-220393), pyraziline derivatives (JP-A-2-220394),cyclopentadiene derivatives (JP-A-2-289675), pyrrolopyrrol derivatives(JP-A-2-296891), styrylamine derivatives (Appl. Phys. Lett., Vol. 56,799 (1990)), coumarin compounds (JP-A-2-191694), and polymer compoundsdisclosed in W090/13148 and Appl. Phys. Lett., vol. 58, 18, p. 1982(1991).

The material for the light-emitting layer is particularly preferablyselected from aromatic dimethylidyne compounds (disclosed in EuropeanPatent 0388768 and JP-A-3-231970). Specific examples thereof include1,4-phenylenedimethylidyne, 4,4'-phenylenedimethylidyne,2,5-xylylenedimethylidyne, 2,6-naphthyldimethylidyne,1,4-biphenylenedimethylidyne, 1,4-p-terphenylenedimethylidyne,9,10-anthracendiyldimethylidyne,4,4'-bis(2,2-di-tert-butylphenylvinyl)biphenyl (to be abbreviated asDTBPVBi hereinafter), 4,4'-bis(2,2-diphenylvinyl)biphenyl (to beabbreviated as DPVBi hereinafter), and derivatives of these.

The light-emitting layer can be formed from the above material, forexample, by any one of known methods such as a vapor deposition method,a spin coating method, a casting method and an LB method. Thelight-emitting layer is particularly preferably a molecular depositionfilm. The term "molecular deposition film" refers to a thin film formedby deposition from a raw material compound in a gaseous state or a filmformed by solidification from a material compound in a solution state orin a liquid phase state. This molecular deposition film is generallydistinguishable from a thin film formed by the LB method (molecularbuilt-up film) due to differences in aggregation structure andhigh-order structure and subsequent functional differences.

Further, as disclosed in JP-A-57-51781, the light-emitting layer can bealso formed by dissolving a binder such as a resin and a materialcompound in a solvent to prepare a solution and forming a thin film fromthe solution.

The film thickness of the so-formed light-emitting layer is notspecially limited, and can be determined as required, while it isgenerally preferably in the range of 5 nm to 5 μm.

The light-emitting layer of the organic EL device has an injectionfunction with which holes can be injected from an anode or thehole-injecting layer and electrons can be injected from a cathode or theelectron-injecting layer when an electric filed is applied, atransportation function with which injected charge (electrons and holes)is carried by the force of the electric field and a light emissionfunction with which a field for the recombination of electrons and holesis provided to generate light emission. There can be a differencebetween the ease with which holes are injected and the ease with whichelectrons are injected. Further, there can be a difference between themobility of holes and the mobility of electrons which represent thetransportation function, while it is preferred that at least ones ofthese should be moved.

The material for the anode is preferably selected from metal, alloys,electrically conductive compounds and mixtures of these, which all havea large work function (at least 4 eV). Specific examples thereof includemetals such as Au and dielectric transparent materials such as CuI, ITO,SnO₂ and ZnO. The anode can be produced by forming a thin film from anyone of the above materials by a vapor deposition method or a sputteringmethod.

When light emitted from the light-emitting layer is transmitted throughthe anode, the transmittance of the anode is preferably larger than 10%.The sheet resistance of the anode is preferably several hundreds Ω/□ orless. Although differing depending upon materials, the thickness of theanode is generally in the range of 10 nm to 1 μm, preferably 10 to 200nm.

The material for the hole-injecting layer which is optionally providedis selected from photoconductive materials conventionally used ashole-injecting materials and known materials used for hole-injectinglayers of organic EL devices. The material for the hole-injecting layerhas any one of hole injection performance and barrier performanceagainst electrons, and it may be any one of an organic material and aninorganic material.

Specific examples thereof include triazole derivatives (see U.S. Pat.No. 3,112,197), oxadiazole derivatives (see U.S. Pat. No. 3,189,447),imidazole derivatives (see Japanese Patent Publication No. 37-16096),polyarylalkane derivatives (see U.S. Pat. No. 3,615,402, U.S. Pat. No.3,820,989, U.S. Pat. No. 3,542,544, JP-B-45-555, JP-B-51-10983,JP-A-51-93224, JP-A-55-17105, JP-A-56-4148, JP-A-55-108667,JP-A-55-156953 and JP-A-56-36656), pyrazoline derivatives and pyrazolonederivatives (see U.S. Pat. No. 3,180,729, U.S. Pat. No. 4,278,746,JP-A-55-88064, JP-A-55-88065, JP-A-49-105537, JP-A-55-51086,JP-A-56-80051, JP-A-56-88141, JP-A-57-45545, JP-A-54-112637 andJP-A-55-74546), phenylenediamine derivatives (see U.S. Pat. No.3,615,404, JP-B-51-10105, JP-B-46-3712, JP-B-47-25336, JP-A-54-53435,JP-A-54-110536 and JP-A-54-119925), arylamine derivatives (see U.S. Pat.No. 3,567,450, U.S. Pat. No. 3,180,703, U.S. Pat. No. 3,240,597, U.S.Pat. No. 3,658,520, U.S. Pat. No. 4,232,103, U.S. Pat. No. 4,175,961,U.S. Pat. No. 4,012,376, JP-B-49-35702, Japanese Patent Publication No.39-27577, JP-A-55-144250, JP-A-56-119132, JP-A-56-22437 and West GermanyPatent 1,110,518), amino-substituted chalcone derivatives (see U.S. Pat.No. 3,526,501), oxazole derivatives (those disclosed in U.S. Pat. No.3,257,203), styrylanthracene derivatives (see JP-A-56-46234), fluorenonederivatives (see JP-A-54-110837), hydrazone derivatives (see U.S. Pat.No. 3,717,462, JP-A-54-59143, JP-A-55-52063, JP-A-55-52064,JP-A-55-46760, JP-A-55-85495, JP-A-57-11350, JP-A-57-148749 andJP-A-2-311591), stilbene derivatives (see JP-A-61-210363,JP-A-61-228451, JP-A-61-14642, JP-A-61-72255, JP-A-62-47646,JP-A-62-36674, JP-A-62-10652, JP-A-62-30255, JP-A-60 -93445,JP-A-60-94462, JP-A-60-174749 and JP-A-60-175052), silazane derivatives(see U.S. Pat. No. 4,950,950), polysilanes (JP-A-2-204996), anilnecopolymers (JP-A-2-282263), and elecytrically conductive high-molecularweight oligomers (particularly thiophene oligomers) disclosed inJP-A-1-211399.

The above compounds can be used as a material for the hole-injectinglayer. It is preferred to use porphyrin compounds (those disclosed inJP-A-63-295695), aromatic tertiary amine compounds and styrylaminecompounds (see U.S. Pat. No. 4,127,412, JP-A-53-27033, JP-A-54-58445,JP-A-54-149634, JP-A-54-64299, JP-A-55-79450, JP-A-55-144250,JP-A-56-119132, JP-A-61-295558, JP-A-61-98353 and JP-A-63-295695), andit is particularly preferred to use aromatic tertiary amine compounds.

Typical examples of the above porphyrin compounds include porphine,1,10,15,20-tetraphenyl-21H,23H-porphine copper (II),1,10,15,20-tetraphenyl-21H,23H-porphine zinc (II),5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-prophine, siliconephthalocyanine oxide, aluminum phthalocine (metal-free), dilithiumphthalocyanine, copper tetramethylphthalocyanine, copper phthalocyanine,chromium phthalocyanine, zinc phthalocyanine, lead phthalocyanine,titanium phthalocyanine, Mg phthalocyanine and copperoctamethylphthalocyanine.

Typical examples of the above aromatic tertiary amine compounds andstyrylamine compounds include N,N,N',N'-tetraphenyl-4,4'-diaminophenyl,N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (tobe abbreviated as TPD hereinafter),2,2-bis(4-di-p-tolylaminophenyl)propane,1,1-bis(4-di-p-tolylaminophenyl)cyclohexane,N,N,N',N'-tetra-p-tolyl-4,4'-diaminobiphenyl,1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane,bis(4-dimethylamino-2-methylphenyl)phenylmethane,bis(4-di-p-tolylaminophenyl)phenylmethane,N,N'-diphenyl-N,N'-di-(4-methoxyphenyl)-4,4'-diaminobiphenyl,N,N,N',N'-tetraphenyl-4,4'-diaminodiphenyl ether,4,4'-bis(diphenylamino)quadriphenyl, N,N,N-tri(p-tolyl)amine,4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)styryl]stilbene,4-N,N-diphenylamino-(2-diphenylvinyl)benzene,3-methoxy-4'-N,N-diphenylaminostyrylbenzene, and N-phenyl carbazole.

The above aromatic dimethylidyne compounds descibed as the material forthe light-emitting layer can be also used as a mateiral for thehole-injecting layer.

The hole-injecting layer can be produced, for example, by forming a thinfilm from any one of the above materials by a known method such asvacuum deposition method, a spin coating method, a casting method or anLB method. The film thickness of the hole-injecting layer is notspecially limited, while it is generally 5 nm to 5 μm. Thehole-injecting layer may have a single-layered structure formed of atleast one of the above materials or a multi-layered structure of thesame composition or different compositions.

The electron-injecting layer which is optionally provided has only tohave the function of transporting electrons injected from a cathode tothe light-emitting layer. The material therefor can be selected fromknown compounds as required.

Specific examples thereof includes nitro-substituted fluorenonederivatives disclosed in JP-A-57-149259, anthraquinodimethanederivatives disclosed in JP-A-58-55450 and JP-A-63-104061,diphenylquinone derivatives disclosed in Polymer Preprints, Japan, Vol.37, No. 3 (1988), page 681, thiopyran dioxide derivatives, heterocyclictetracarboxylic acid anhydrides such as naphthalene perylene,carbodiimide, fluorenylidenemethane derivatives disclosed in JapaneseJournal of Applied Physics, 27, L 269 (1988), JP-A-60-69657,JP-A-61-143764 and JP-A-61-148159, anthraquinodimethane derivatives andanthrone derivatives disclosed in JP-A-61-225151 and JP-A-61-233750,oxadiazole derivatives disclosed in Appl. Phys. Lett., 55, 15, 1489 orby Hamada et al., in the aforesaid Proceedings of No. 38th SpringMeeting 1993 The Japan Society of Applied Physics and Related Society,and series of electron-conducting compounds disclosed in JP-A-59-194393.In addition, JP-A-59-194393 discloses the above electron-conductingcompounds as materials for the light-emitting layer, while the study ofthe present inventors has revealed that they can be also used asmaterials for the electron-injecting layer.

The material for the electron-injecting layer can be also selected frommetal complexes of 8-quinolinol derivatives. Specific examples thereofinclude tris(8-quinolinol)aluminum,tris(5,7-dichloro-8-quinolinol)aluminum,tris(5,7-dibromo-8-quinolinol)aluminum,tris(2-methyl-8-quinolinol)aluminum and the same metal complexes asthose except that the central metal is replaced with In, Mg, Cu, Ca, Snor Pb.

Further, the material for the electron-injecting layer is alsopreferably selected from metal-free phthalocyanine, metal phthalocyanineand the same metal-free or metal phthalocyanine whose terminal isreplaced with an alkyl group or sulfone group. The distyrylpyrazinederivatives described as the materials for the light-emitting layer canbe also used as materials for the electron-injecting layer.

The electron-injecting layer can be produced, for example, by forming athin film from any one of the above materials by a known method such asvacuum deposition method, a spin coating method, a casting method or anLB method. The film thickness of the electron-injecting layer is notspecially limited, while it is generally 5 nm to 5 μm. Theelectron-injecting layer may have a single-layered structure formed ofat least one of the above materials or a multilayered structure of thesame composition or different compositions.

The material for the hole-injecting layer can be also selected fromhole-injecting and transporting materials formed of inorganic compoundssuch as p-type-Si and p-type SiC, and the material for theelectron-injecting layer can be also selected from electron-injectionand transporting materials formed of inorganic compounds such as n-typeSi and n-type-SiC. Specific examples of the inorganic materials for thehole-injecting layer and the inorganic materials for theelectron-injecting layer are those inorganic semiconductors disclosed inInternational Laid-open Publication W090/05998.

The organic EL device of the present invention, which can be produced byforming the light-emitting layer, the anode, the optional hole-injectinglayer and the optional electron-injecting layer from the above-describedmaterials by the above-described methods and forming the cathode by theabove-described method, may have any constitution as described above.The following is a brief explanation of one embodiment of the productionof an organic EL device having a constitution of anode on asubstrate/hole-injecting layer/light-emitting layer/cathode.

First, the anode is produced on a proper substrate by forming a thinfilm from the anode material by a vapor deposition method, a sputteringmethod, etc., such that the film thickness is 1 μm or less, preferablyin the range of 10 to 200 nm. Then, the hole-injecting layer is formedon the anode. As described above, the hole-injecting layer can be formedby a vacuum deposition method, a spin coating method, a casting methodor an LB method, while it is preferably formed by a vacuum depositionmethod since a homogeneous film can be easily obtained and since thismethod is almost free from the formation of pin holes. When thehole-injecting layer is formed by a vacuum deposition method, the vapordeposition conditions differ depending upon an employed compound(material for the hole-injecting layer) and the crystal structure andaggregation structure of the intended hole-injecting layer. Generally,however, it is preferred to select the deposition conditions from thefollowing ranges as required. The temperature of the vapor depositionsource is 50° to 450° C., the vacuum degree is 10⁻⁵ to 10⁻³ Pa, thedeposition rate is 0.01 to 50 nm/sec., the substrate temperature is -50°to 300° C., and the film thickness is 5 nm to 5 μm.

Then, the light-emitting layer is formed on the above hole-injectinglayer. The light-emitting layer can be also formed from a desiredorganic light-emitting material by a vacuum deposition method, a spincoating method, a casting method, etc., while it is preferably formed bya vacuum deposition method since a homogeneous film can be easilyobtained and since this method is almost free from the formation of pinholes. When the light-emitting layer is formed by a vacuum depositionmethod, the vapor deposition conditions differ depending upon a compoundused, while they are generally selected from the same condition rangesas the above-described conditions concerning the hole-injecting layer.

After the light-emitting layer is formed, the cathode is formed on theabove light-emitting layer by vapor-depositing the metal A and the metalB by multi-source simultaneous vapor deposition, whereby the intendedorganic EL device can be obtained.

The vapor deposition conditions for forming the cathode by themulti-source simultaneous vapor deposition of the metal A and the metalB differ depending upon the kinds of the metal A and the metal B.Generally, however, it is preferred to select the deposition conditionsfrom the following ranges as required. The temperature of the vapordeposition source is 100° to 5,000° C., the vacuum degree is 1×10⁻² Paor less, and the substrate temperature is -200° to 500° C. As alreadydescribed, the deposition rate of the metal A is at least 2 nm/sec.,particularly at least 4 nm/sec., and the deposition rate of the metal Bis 0.5 nm/sec. or less, particularly 0.2 nm/sec. The film thickness ofthe cathode is preferably 10 to 400 nm, particularly preferably 30 to200 nm, as already described. In the production of this organic ELdevice, the production order may be reversed, and it can be produced inthe order of cathode on a substrate/light-emitting layer/hole-injectinglayer/anode.

When a direct-current voltage is applied to the organic EL device of thepresent invention, a voltage of 5 to 40 V is applied with setting thepolarity of the anode as + (plus) and that of the cathode as - (minus),whereby light emission is observed. When a voltage is applied withsetting the polarity reversely, no current appears, and no lightemission is generated. Further, when an alternate current is charged,uniform light emission is observed only when the anode is in thepolarity of + and the cathode is in the polarity of -. The waveform ofthe alternate current charged may be as required.

Examples of the present invention will be explained hereinafter.

EXAMPLE 1 (Organic EL device having Pb-Mg cathode)

A glass plate having a size of 25×75×1.1 mm on which a 100 nm thick ITOfilm (corresponding to anode) was formed was used as a transparentsubstrate. This transparent substrate was subjected to ultrasoniccleaning with isopropyl alcohol for 5 minutes, and then cleaned withpure water for 5 minutes. Further, it was subjected to ultrasoniccleaning with isopropyl alcohol for 5 minutes.

The cleaned transparent substrate was fixed on a substrate holder in acommercially available vacuum deposition apparatus (supplied by NihonShinku Gijutsu K.K.]. And, 200 mg ofN,N'-diphenyl-N,N'-bis-(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (tobe referred to as "TPD" hereinafter) was placed in a molybdenumresistance heating boat, and 200 mg of4,4'-bis(2,2-diphenylvinyl)biphenyl (to be referred to as "DPVBi"hereinafter) was placed in other molybdenum resistance heating boat. Thepressure in the vacuum chamber was reduced to 1×10⁻⁴ Pa.

Then, the molybdenum resistance heating boat in which TPD was placed washeated up to 215° to 220° C. to deposit TPD on the ITO film of thetransparent substrate at a deposition rate of 0.1 to 0.3 nm/sec.,whereby a hole-injecting layer having a thickness of 60 nm was formed.At this time, the substrate had a temperature of room temperature. Then,while the transparent substrate was allowed to stay without taking itout of the vacuum chamger, the above molybdenum resistance heating boatin which DPVBi was placed was heated up to 220° C. to deposit DPVBi onthe hole-injecting layer at a deposition rate of 0.1 to 0.2 nm/sec.,whereby a light-emitting layer having a thickness of 40 nm was formed.At this time, the substrate also had a temperature of room temperature.

The substrate on which the anode, hole-injecting layer andlight-emitting layer were consecutively formed above was taken out ofthe vacuum chamber, and after a mask of stainless steel was placed onthe above light-emitting layer, the substrate was fixed on the substrateholder again. Then, 200 mg of tris(8-quinolinol)aluminum (Alq.) wasplaced in a molybdenum resistance heating boat, and the molybdenumresistance heating boat was set in the vacuum chamber. Further, 8 g of aPb ingot was placed in a basket of alumina-coated tungsten, and 1 g of aribbon of Mg (work function 3.68 eV) was placed in other molybdenumboat.

Thereafter, the pressure in the vacuum chamber was reduced to 2×10⁻⁴ Pa,and the boat in which Alq. was placed was heated to 280° C. by applyingelectricity to deposit Alq. at a deposition rate of 0.3 nm/sec., wherebyan electron-injecting layer having a thickness of 20 nm was formed.

Then, Pb as the metal A and Mg as the metal B were simultaneouslyvapor-deposited at a metal A deposition rate of 9 nm/sec. and metal Bdeposition rate of 0.04 nm/sec. to form a cathode of a Pb-Mg vapordeposited film having a thickness of 200 nm. The anode, hole-injectinglayer, light-emitting layer, electron-injecting layer and cathode wereformed on the glass substrate as above, whereby an organic EL device wasobtained.

The composition ratio of Pb and Mg forming the cathode was calculated onthe basis of vapor deposition ratio by the following expression.##EQU1##

When a direct-current voltage of 7 V (current density: 2.5 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, blue uniform light emission at 44 cd/m² was observed. The powerconversion efficiency at this time was as high as 0.78 lumen (lm)/W asshown in Table 1. Further, the organic EL device was allowed to stand inair for 6 months. Then, the state of the cathode was examined to show nochange as shown in Table 1, and it was excellent in chemical stabilitywith time.

EXAMPLE 2 (Organic EL device having Pb-Ca cathode)

An organic EL device was obtained in the same manner as in Example 1except that Ca (work function 2.9) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Pb as metal A was set at 8.8 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.4 at. % of Pband 1.6% of Ca.

Further, when a direct-current voltage of 7 V (current density: 2.1mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 44 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.91 lumen(lm)/W as shown in Table 1. Further, the cathode was excellent inchemical stability with time as shown in Table 1.

EXAMPLE 3 (Organic EL device having Pb-Li cathode)

An organic EL device was obtained in the same manner as in Example 1except that Li (work function 2.93) was used as metal B, that thedeposition rate of the metal B was set at 0.04 nm/sec., and that thedeposition rate of Pb as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.4 at. % of Pband 0.6 at. % of Li.

Further, when a direct-current voltage of 7 V (current density: 4.9mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 84 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.77 lumen(lm)/W as shown in Table 1. Further, the cathode was excellent inchemical stability with time as shown in Table 1.

EXAMPLE 4 (Organic EL device having Pb-Mg cathode)

An organic EL device was obtained in the same manner as in Example 1except that Mg (work function 3.68) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Pb as metal A was set at 5 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 95 at. % of Pband 5 at. % of Mg.

Further, when a direct-current voltage of 7 V (current density: 1.1mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 20 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.82 lumen(lm)/W as shown in Table 1. Further, the cathode was excellent inchemical stability with time as shown in Table 1.

Comparative Example 1

An organic EL device was obtained in the same manner as in Example 1except that the metal B was replaced with Au (work function 5.1), thatthe deposition rate thereof was set at 0.04 nm/sec., and that thedeposition rate of Pb as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.3 at. % of Pband 0.7 at. % of Au.

Further, a direct-current voltage of 12 V (current density: 6.3 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.0083 lumen (lm)/W as shown in Table1.

Comparative Example 2

An organic EL device was obtained in the same manner as in Example 1except that the metal B was replaced with Ni (work function 5.15), thatthe deposition rate thereof was set at 0.04 nm/sec., and that thedeposition rate of Pb as metal A was set at 8.3 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.8 at. % of Pband 1.2 at. % of Ni.

Further, a direct-current voltage of 15 V (current density: 49 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.0047 lumen (lm)/W as shown in Table1.

Comparative Example 3

An organic EL device was obtained in the same manner as in Example 1except that no metal B was used and that Pb as metal A wasvapor-deposited at a deposition rate of 13 nm/sec.

A direct-current voltage of 15 V (current density: 16.8 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.0088 lumen (lm)/W as shown in Table1.

Comparative Example 4

An organic EL device was obtained in the same manner as in Example 1except that the Pb as metal A was replaced with Mg, that In included inthe metal B was used, that the deposition rate of Mg was set at 8nm/sec., and that the deposition rate of In was set at 0.06 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.3 at. % of Mgand 0.7 at. % of In.

Further, a direct-current voltage of 7 V (current density: 2.1 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was 0.45 lumen (lm)/W as shown in Table 1. When the aboveorganic EL device was allowed to stand in air for 8 months, the cathodewas oxidized to turn transparent, which shows that the cathode wasinferior in chemical stability with time, as shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Cathode                                                                       Material        Deposition Work function of                                   (compositional  rate       metal other than                                   ratio: at/at)   (nm/sec.)  Pb                                                 ______________________________________                                        Ex. 1 Pb--Mg   (99.3/0.7)                                                                             9:0.04   3.68                                         Ex. 2 Pb--Ca   (98.4/1.6)                                                                             8.8:0.2  2.9                                          Ex. 3 Pb--Li   (99.4/0.6)                                                                             10:0.04  2.93                                         Ex. 4 Pb--Mg   (95/5)   5:0.2    3.68                                         CEx. 1                                                                              Pb--Au   (99.3/0.7)                                                                             10:0.04  5.1                                          CEx. 2                                                                              Pb--Ni   (98.8/1.2)                                                                             8.3:0.04 5.15                                         CEx. 3                                                                              Pb                13       --                                           CEx. 4                                                                              Mg--In   (99.3/0.7)                                                                             8:0.06   --                                           ______________________________________                                                                        Power                                                                         con-   Chemical                                     Charged  Current   Bright-                                                                              version                                                                              stability                                    voltage  density   ness   efficiency                                                                           with time                                    (V)      (mA/cm.sup.2)                                                                           (cd/m.sup.2)                                                                         (lm/W) *                                      ______________________________________                                        Ex. 1 7        2.5       44     0.78   No change                              Ex. 2 7        2.1       44     0.91   No change                              Ex. 3 7        4.9       84     0.77   No change                              Ex. 4 7        1.1       20     0.82   No change                              CEx. 1                                                                              12       6.3       2      0.0083 No change                              CEx. 2                                                                              15       49        11     0.0047 No change                              CEx. 3                                                                              15       16.8      7.1    0.0088 No change                              CEx. 4                                                                              7        10        100    0.45   Electrode                                                                     oxidized                                                                      to be                                                                         transparent                            ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                     *Chemical stability with time was evaluated by observing the state of         electrode (cathode) after organic EL device was allowed to stand in air       for 6 months.                                                            

EXAMPLE 5 (Organic EL device having Sn-Mg cathode)

An anode, a hole-injecting layer, a light-emitting layer and anelectron-injecting layer were formed on a substrate in the same manneras in Example 1.

Then, Sn as metal A and Mg (work function 3.68 eV) as metal B weresimultaneously vapor-deposited at a metal A deposition rate of 9 nm/sec.and a metal B deposition rate of 0.04 nm/sec. to form a cathode of aSn-Mg vapor deposition film having a thickness of 200 nm. The anode,hole-injecting layer, light-emitting layer, electroninjecting layer andcathode were formed on the glass substrate as above, whereby an organicEL device was obtained.

The composition ratio of Sn and Mg was calculated on the basis ofdeposition ratio by the expression shown in Example 1. As a result, theSn content was 99.5%, and the Mg content was 0.5%.

When a direct-current voltage of 7 V (current density: 2.5 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, blue uniform light emission at 42 cd/m² was observed. The powerconversion efficiency at this time was as high as 0.75 lumen (lm)/W asshown in Table 2. Further, the organic EL device was allowed to stand inair for 6 months. Then, the state of the cathode was examined to show nochange as shown in Table 2, and it was excellent in chemical stabilitywith time.

EXAMPLE 6 (Organic EL device having Sn-Ca cathode)

An organic EL device was obtained in the same manner as in Example 5except that Ca (work function 2.9) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Sn as metal A was set at 8.8 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.8 at. % of Snand 1.4% of Ca.

Further, when a direct-current voltage of 7 V (current density: 2.0mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 44 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.98 lumen(lm)/W as shown in Table 2. Further, the cathode was excellent inchemical stability with time as shown in Table 2.

EXAMPLE 7 (Organic EL device having Sn-Li cathode)

An organic EL device was obtained in the same manner as in Example 5except that Li (work function 2.93) was used as metal B, that thedeposition rate of the metal B was set at 0.05 nm/sec., and that thedeposition rate of Sn as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.4 at. % of Snand 0.6 at. % of Li.

Further, when a direct-current voltage of 7 V (current density: 4.9mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 80 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.73 lumen(lm)/W as shown in Table 2. Further, the cathode was excellent inchemical stability with time as shown in Table 2.

EXAMPLE 8 (Organic EL device having Sn-Mg cathode)

An organic EL device was obtained in the same manner as in Example 5except that Mg (work function 3.68) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Sn as metal A was set at 5 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 95.5 at. % of Snand 4.5 at. % of Mg.

Further, when a direct-current voltage of 7 V (current density: 1.3mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 25 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.86 lumen(lm)/W as shown in Table 2. Further, the cathode was excellent inchemical stability with time as shown in Table 2.

Comparative Example 5

An organic EL device was obtained in the same manner as in Example 5except that the metal B was replaced with Au (work function 5.1), thatthe deposition rate thereof was set at 0.05 m/sec., and that thedeposition rate of Sn as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.2 at. % of Snand 0.8 at. % of Au.

Further, a direct-current voltage of 13 V (current density: 7.0 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.01 lumen (lm)/W as shown in Table 2.

Comparative Example 6

An organic EL device was obtained in the same manner as in Example 5except that the metal B was replaced with Ni (work function 5.15), thatthe deposition rate thereof was set at 0.04 nm/sec., and that thedeposition rate of Sn as metal A was set at 8.5 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.9 at. % of Snand 1.1 at. % of Ni.

Further, a direct-current voltage of 15 V (current density: 50 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.005 lumen (lm)/W as shown in Table2.

Comparative Example 7

An organic EL device was obtained in the same manner as in Example 5except that no metal B was used and that Sn as metal A wasvapor-deposited at a deposition rate of 13 nm/sec.

A direct-current voltage of 15 V (current density: 16 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.0092 lumen (lm)/W as shown in Table2.

Comparative Example 8

An organic EL device was obtained in the same manner as in Example 5except that Sn as metal A was replaced with Mg, that In was used asmetal B, that the deposition rate of Mg was set at 8 nm/sec., and thatthe deposition rate of In was set at 0.06 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.3 at. % of Mgand 0.? at. % of In.

Further, a direct-current voltage of ? V (current density: 2.1 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was 0.45 lumen (lm)/W as shown in Table 2. When the aboveorganic EL device was allowed to stand in air for 6 months, the cathodewas oxidized to turn transparent, which shows that the cathode wasinferior in chemical stability with time, as shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Cathode                                                                       Material        Deposition Work function of                                   (compositional  rate       metal other than                                   ratio: at/at)   (nm/sec.)  Sn                                                 ______________________________________                                        Ex. 5 Sn--Mg   (99.5/0.5)                                                                             9:0.04   3.68                                         Ex. 6 Sn--Ca   (98.6/1.4)                                                                             8.8:0.2  2.9                                          Ex. 7 Sn--Li   (99.4/0.6)                                                                             10:0.05  2.93                                         Ex. 8 Sn--Mg   (95.5/4.5)                                                                             5:0.2    3.68                                         CEx. 5                                                                              Sn--Au   (99.2/0.8)                                                                             10:0.05  5.1                                          CEx. 6                                                                              Sn--Ni   (98.9/1.1)                                                                             8.5:0.04 5.15                                         CEx. 7                                                                              Sn                13       --                                           CEx. 8                                                                              Mg--In   (99.3/0.7)                                                                             8:0.06   --                                           ______________________________________                                                                        Power                                                                         con-   Chemical                                     Charged  Current   Bright-                                                                              version                                                                              stability                                    voltage  density   ness   efficiency                                                                           with time                                    (V)      (mA/cm.sup.2)                                                                           (cd/m.sup.2)                                                                         (lm/W) *                                      ______________________________________                                        Ex. 5 7        2.5       42     0.75   No change                              Ex. 5 7        2.0       44     0.98   No change                              Ex. 7 7        4.9       80     0.73   No change                              Ex. 8 7        1.3       25     0.86   No change                              CEx. 5                                                                              13       7.0       3      0.01   No change                              CEx. 6                                                                              15       50        12     0.005  No change                              CEx. 7                                                                              15       16        7.1    0.0092 No change                              CEx. 8                                                                              7        10        100    0.45   Electrode                                                                     oxidized                                                                      to be                                                                         transparent                            ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                     *Chemical stability with time was evaluated by observing the state of         electrode (cathode) after organic EL device was allowed to stand in air       for 6 months.                                                            

EXAMPLE 9 (Organic EL device having Bi-Mg cathode)

An anode, a hole-injecting layer, a light-emitting layer and anelectron-injecting layer were formed on a substrate in the same manneras in Example 1.

Then, Bi as metal A and Mg as metal B were simultaneouslyvapor-deposited at a metal A deposition rate of 9 nm/sec. and a metal Bdeposition rate of 0.04 nm/sec. to form a cathode of a Bi-Mg vapordeposition film having a thickness of 200 run. The anode, hole-injectinglayer, light-emitting layer, electron-injecting layer and cathode wereformed on the glass substrate as above, whereby an organic EL device wasobtained.

The composition ratio of Bi and Mg was calculated on the basis ofdeposition ratio by the expression shown in Example 1. As a result, theBi content was 99.3%, and the Mg content was 0.7%.

When a direct-current voltage of 7 V (current density: 2.6 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, blue uniform light emission at 45 cd/m² was observed. The powerconversion efficiency at this time was as high as 0.78 lumen (lm)/W asshown in Table 3. Further, the organic EL device was allowed to stand inair for 6 months. Then, the state of the cathode was examined to show nochange as shown in Table 3, and it was excellent in chemical stabilitywith time.

EXAMPLE 10 (Organic EL device having Bi-Ca cathode)

An organic EL device was obtained in the same manner as in Example 9except that Ca (work function 2.9) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Bi as metal A was set at 8.8 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.1 at. % of Biand 1.9% of Ca.

Further, when a direct-current voltage of 7 V (current density: 2.2mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 50 cd/m² was observed. Thepower conversion efficiency at this time was as high as 1.00 lumen(lm)/W as shown in Table 3. Further, the cathode was excellent inchemical stability with time as shown in Table 3.

EXAMPLE 11 (Organic EL device having Bi-Li cathode)

An organic EL device was obtained in the same manner as in Example 9except that Li (work function 2.93) was used as metal B, that thedeposition rate of the metal B was set at 0.05 nm/sec., and that thedeposition rate of Bi as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.2 at. % of Biand 0.8 at. % of Li.

Further, when a direct-current voltage of 7 V (current density: 5.0mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 100 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.90 lumen(lm)/W as shown in Table 3. Further, the cathode was excellent inchemical stability with time as shown in Table 3.

EXAMPLE 12 (Organic EL device having Bi-Mg cathode)

An organic EL device was obtained in the same manner as in Example 9except that Mg (work function 3.68) was used as metal B, that thedeposition rate of the metal B was set at 0.2 nm/sec., and that thedeposition rate of Bi as metal A was set at 5 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 94.2 at. % of Biand 5.8 at. % of Mg.

Further, when a direct-current voltage of 7 V (current density: 1.4mA/cm²) was applied to the above-obtained organic EL device with settingthe polarity of the cathode as - and the polarity of the anode (ITOfilm) as +, blue uniform light emission at 22 cd/m² was observed. Thepower conversion efficiency at this time was as high as 0.71 lumen(lm)/W as shown in Table 3. Further, the cathode was excellent inchemical stability with time as shown in Table 3.

Comparative Example 9

An organic EL device was obtained in the same manner as in Example 9except that the metal B was replaced with Au (work function 5.1), thatthe deposition rate thereof was set at 0.05 nm/sec., and that thedeposition rate of Bi as metal A was set at 10 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.0 at. % of Biand 1.0 at. % of Au.

Further, a direct-current voltage of 13 V (current density: 7.0 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.017 lumen (lm)/W as shown in Table3.

Comparative Example 10

An organic EL device was obtained in the same manner as in Example 9except that the metal B was replaced with Ni (work function 5.15), thatthe deposition rate thereof was set at 0.04 nm/sec., and that thedeposition rate of Bi as metal A was set at 8.5 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 98.5 at. % of Biand 1.5 at. % of Ni.

Further, a direct-current voltage of 15 V (current density: 50 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.0046 lumen (lm)/W as shown in Table3.

Comparative Example 11

An organic EL device was obtained in the same manner as in Example 9except that no metal B was used and that Bi as metal A wasvapor-deposited at a deposition rate of 13 nm/sec,

A direct-current voltage of 15 V (current density: 16 mA/cm²) wasapplied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was very low, as low as 0.01 lumen (lm)/W as shown in Table 3.

Comparative Example 12

An organic EL device was obtained in the same manner as in Example 9except that Bi as metal A was replaced with Mg, that In was used asmetal B, that the deposition rate of Mg was set at 8 nm/sec., and thatthe deposition rate of In was set at 0.06 nm/sec.

The composition of the cathode of the above-obtained organic EL devicewas calculated to show that the cathode was composed of 99.3 at. % of Mgand 0.7 at. % of In.

Further, a direct-current voltage of 7 V (current density: 10 mA/cm²)was applied to the above-obtained organic EL device with setting thepolarity of the cathode as - and the polarity of the anode (ITO film) as+, and light emission was observed. The power conversion efficiency atthis time was 0.45 lumen (lm)/W as shown in Table 3. When the aboveorganic EL device was allowed to stand in air for 6 months, the cathodewas oxidized to turn transparent, which shows that the cathode wasinferior in chemical stability with time, as shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Cathode                                                                       Material         Deposition                                                                              Work function of                                   (compositional   rate      metal other than                                   ratio: at/at)    (nm/sec.) Bi                                                 ______________________________________                                        Ex. 9  Bi--Mg   (99.3/0.7)                                                                             9:0.04  3.68                                         Ex. 10 Bi--Ca   (98.1/1.9)                                                                             8.8:0.2 2.9                                          Ex. 11 Bi--Li   (99.2/0.8)                                                                             10:0.05 2.93                                         Ex. 12 Bi--Mg   (94.2/5.8)                                                                             5:0.2   3.68                                         CEx. 9 Bi--Au   (99.0/1.0)                                                                             10:0.05 5.1                                          CEx. 10                                                                              Bi--Ni   (98.5/1.5)                                                                             8.5:0.04                                                                              5.15                                         CEx. 11                                                                              Bi                13      --                                           CEx. 12                                                                              Bi--In   (99.3/0.7)                                                                             8:0.06  --                                           ______________________________________                                                                        Power                                                         Current         con-   Chemical                                      Charged  density  Bright-                                                                              version                                                                              stability                                     voltage  (mA/     ness   efficiency                                                                           with time                                     (V)      cm.sup.2)                                                                              (cd/m.sup.2)                                                                         (lm/W) *                                      ______________________________________                                        Ex. 9  7        2.6      45     0.78   No change                              Ex. 10 7        2.2      50     1.00   No change                              Ex. 11 7        5.0      100    0.90   No change                              Ex. 12 7        1.4      22     0.71   No change                              CEx. 9 13       7.0      5      0.017  No change                              CEx. 10                                                                              15       50       11     0.0046 No change                              CEx. 11                                                                              15       16       8      0.01   No change                              CEx. 12                                                                              7        10       100    0.45   Electrode                                                                     oxidized                                                                      to be                                                                         transparent                            ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                     *Chemical stability with time was evaluated by observing the state of         electrode (cathode) after organic EL device was allowed to stand in air       for 6 months.                                                            

As explained above, the present invention provides a novel organic ELdevice which has a cathode highly chemical stable with time and exhibitsimproved power conversion efficiency.

We claim:
 1. An organic Electroluminescence device comprising a cathode,an anode and an organic light-emitting material disposed between saidcathode and said anode, wherein said cathode is formed by a vapordeposited film containing (a) at least one metal A selected from thegroup consisting of Pb, Sn and Bi and (b) at least one metal B selectedfrom the group consisting of Li, Ba, La, Ca, Na, K, Y, Mg and Yb, saidcathode having a metal A content of 95 to 99.99 at. %.
 2. The organicelectroluminescence device according to claim 1, wherein the metal B isat least one metal selected from the group consisting of Ca, Ba and Yb.3. The organic electroluminescence device according to claim 1, whereinthe metal B is Li.
 4. The organic electroluminescence device accordingto claim 1, wherein the metal A is Pb and the metal B is Li.
 5. Theorganic electroluminescence device according to claim 1, wherein theorganic light-emitting material is selected from the group consisting ofbenzothiazole, benzoimidazole, a benzooxazole fluorescent brightener, ametal chelated oxinoid compound and a styrylbenzene compound.
 6. Theorganic electroluminescence device according to claim 1, wherein theorganic light-emitting material has a film thickness of 5 nm to 5 μm. 7.The organic electroluminescence device according to claim 6, wherein theanode has a thickness of 10 nm to 10 μm.
 8. The organicelectroluminescence device according to claim 6, wherein the anode has athickness of 10 to 200 nm.
 9. The organic electroluminescence deviceaccording to claim 8, wherein the anode has a work function of at least4 eV.
 10. The organic electroluminescence device according to claim 9,wherein the anode comprises Au, CuI, ITO, SnO₂ or Zn.